John Schmitt wrote:
On Wed, 19 Oct 2005 14:03:07 +0100, Stuart Noble
wrote:


Oxalic acid only really applies to rust stains as it tends to take
out the hydrated oxides of iron.


It seems to be the basis of decking cleaners (a new must-have for the
makeover brigade). Quite what it does, and how, isn't immediately clear.
I've never found it effective as a wood bleach.


It will not as such bleach wood. However, oak (a common deck wood)
stains a dark colour on exposure to iron salts, the tannins in the oak
will react with them. Leave a piece of iron or steel on the deck and
give it a bit of salt spray and you have a deeply rooted stain. Again
the oxalic acid forms a metastable complex which is colourless. Being
metastable, the colour will return in time and require a further
application.

John Schmitt


I imagine most of what people would want to clean from decking wouldn't
be iron stains, and most of the decking wouldn't be hardwood. So, what
else is special about oxalic that it's sold as a cleaner for decking,
the bulk of which is likely to be softwood?